FIG. 1 schematically and by a solid line shows an embodiment of a prior art seat valve which has been used for a long time. Such a prior art valve (2, 4) is constituted by a face (6) of a preferably round valve body (2) and an outlet area (4) of an opening (5) in a counterpart (1). The valve (2, 4) is shown in a closed state. In the closed state, the face (6) presses sealingly on the outlet area (4). The valve (2, 4) is opened by an opening stroke s produced in a suitable and known manner on the valve body (2), as indicated by an arrow. The valve (2, 4) is closed by a closing stroke of the valve body in the opposite direction.
FIG. 6 shows the valve cross-section F, i.e., the passage cross-section of the valve (2, 4), in the form of a line a as a function of the opening stroke s. The valve cross-section F is a cylindrical surface proportional to the opening stroke s. Therefore, line a is a straight line. Considerable throughput of flow medium, even within the range of short opening strokes s, is allowed through the valve because the gradient of this straight line remains constant from the beginning of the opening of the valve (2, 4). Although generally desirable, such a characteristic is disadvantageous for some applications. For example, if the valve (2, 4) is to be used for a fine-tuned adjustment of the flow medium throughput and/or of the flow medium pressure, this characteristic is disadvantageous.
For this reason the valve (2, 4) has been further developed by providing an extension on the face (6) which dips into the opening (5). Such an extension (3) is indicated by a broken line in FIG. 1. The extension (3) is conical. This extension makes it possible to obtain a characteristic curve of the valve area F along line b in FIG. 6. All other conditions remain unchanged. This characteristic curve b has a considerably lower gradient within the range of short opening strokes s than does line a. A significant reduction of the original flow medium throughput is thereby produced. This reduction improves the performance of critical applications and makes it possible to use the valve (2, 4) in critical applications.
However, even the further development in form of an extension (3) on the face (6) of the valve (2, 4) is not sufficient to ensure satisfactory performance for all applications.